The German patent specification DE 101 39 139 A1 relates to a metering system for metering a reducing agent for the after treatment of exhaust gases. The reducing agent particularly relates to urea, respectively a urea-water solution. Said reducing agent is used to reduce the nitrogen oxides contained in the exhaust gas of an internal combustion engine. The apparatus comprises a delivery device for transporting said reducing agent from a storage tank to an exhaust pipe carrying the exhaust gas. In addition, the apparatus comprises an apportioning device for metering the supply of said reducing agent into the exhaust pipe. The delivery device thereby contains a pump and the apportioning device a proportioning valve having an outlet element. The apportioning device is designed such that it can be attached close to or to the exhaust pipe; thus enabling the outlet element to project into said exhaust pipe. Said delivery device is constructed in such a way that it can be accommodated on or inside the storage tank for said reducing agent, and said delivery device and said apportioning device form modules which are separated from each other and are connected to each other by a connecting line.
The German patent specification DE 10 2004 051 746 A1 relates to a reservoir module for a reducing agent and to a metering system. According to this solution, the reservoir module comprises at least one reservoir module housing. A metering system for metering a reducing agent into an exhaust gas system is arranged inside a reservoir chamber of the reservoir module housing.
The German patent specification DE 10 2006 027 487 A1 relates to a vehicle tank for a liquid reducing agent, particularly for a urea solution. The vehicle tank for a liquid, for example aqueous, reducing agent, in particular for a urea solution, for the reduction of nitrogen oxides in the exhaust gas of internal combustion engines has a container wall which is manufactured from plastic material.
If need be, the reducing agent stored in the tank has to be thawed in order to employ a metering system for the metering of urea or an aqueous urea-water solution for the reduction of nitrogen oxides in the exhaust gas of an internal combustion engine and to assure that said metering system functions at low temperatures. For that reason, the tank for storing the reducing agent is as a rule equipped with a heater, particularly an electrically operated heater. Furthermore, the storage tank for receiving the reducing agent includes a level (fill-level) sensor as well as a temperature sensor. An aeration and ventilation of the storage tank occur via a venting system associated with said tank.
The tank bladder of the storage tank normally has the following openings:
an opening for filling the storage tank,
an opening for installing the heating element and the sensors,
in addition an opening for the supply line and return line of the delivery module,
an opening for venting the tank as well as
an opening for emptying the storage tank.
These openings can be positioned at various locations on the storage tank. For reasons of a simplified installation, the module “heating element, fill-level sensor, temperature sensor” is mounted on the bottom thereof, respectively can be dismantled therefrom. The suction line is also usually attached at the lowest point of the tank. Because the ice first thaws around the heater located at the bottom of the tank, it is useful to also carry out the venting of the tank from the bottom side. The openings for emptying the tank are advantageously placed at the deepest point thereof. For this variety of reasons, the openings mentioned above are normally placed on the bottom side of the tank.
This, however, has the disadvantage that all of the above mentioned openings in the tank bladder lie below the fluid level of the reducing agent. Because the reducing agent used, in particular the urea-water solution, is a medium particularly capable of creep, leaks occur more frequently at these openings. This is especially true for plastic tanks, which compared to stainless steel tanks demonstrate instability as a result of external influences, accelerations, ice pressure and thermal stress. Because the aqueous urea solution on the one hand changes immediately to crystals when coming in contact with the air and on the other hand leads to severe corrosion of elastomer plastics and metallic materials, even the smallest leak automatically gives rise to a claim.